what's the source IP of the host you're port forwarding traffic from? Out on the Internet, or on a private network? my first guess is you're forwarding in from a 192.168.x.x network and hosts with a /16 mask see that as a local network, which means the replies won't go anywhere.

Yes it has a valid wan ip, and I can access the internet via internal devices on both /24 and /16 subnets, but the really odd part is that the ports forwards work fine if I change the device to a /24.

Right now the websites in question are available and being used (Because I switched their internal ip to a /24), but it is really annoying to have to segment parts of our internal network for no logical reason.